Frequently, overfilled arch structures formed of precast or cast-in-place reinforced concrete are used in the case of bridges to support one pathway over a second pathway, which can be a waterway, a traffic route, or in the case of other structures, a storage space of the like. The terms “overfilled arch” or “overfilled bridge” will be understood from the teaching of the present disclosure, and in general as used herein, an overfilled bridge or an overfilled arch is a bridge formed of arch elements that rest on the ground or on a foundation and has soil or the like resting thereon and thereabout to support and stabilize the structure and in the case of a bridge provide the surface of the second pathway. The arch form is generally arcuate such as cylindrical in circumferential shape, and in particular a prolate shape; however, other shapes can be used. Examples of overfilled bridges are disclosed in U.S. Pat. Nos. 3,482,406 and 4,458,457, the disclosures of which are incorporated herein by reference.
Presently, reinforced concrete overfilled arches are usually constructed by either casting the arch in place or placing precast elements. These arched structures rest on prepared foundations at the bottom of both sides of the arch. The fill material, at the sides of the arch (backfill material) serves to diminish the outward displacements of the structures when the structure is loaded from above. As used herein, the term “soil” is intended to refer to the normal soil, which can be “backfill” (soil brought to and placed in location) or “in situ” (soil in its original location). Such soil is not adequate to support the concentrated loads at the ends of a flat arch or conventional arch without load distribution through the use of arch footings and/or reinforced foundation blocks.
For the prior art structures, overfilled arches are normally formed such that the foundation level of the arch is at the approximate level of a lower pathway or floor surface of an underground structure over which the arch spans. Referring to FIGS. 1A-1C, it can be understood that prior art systems S1 and S2 include sides or sidewalls SW1 and SW2 which transfer loads from tops T1 and T2 of the arch to foundation F1 and F2. The sides of arch systems S1 and S2 must be sufficiently thick and contain sufficient reinforcement in order to be able to carry these loads and the thereby induced bending moments.
Furthermore, as it is necessary to limit the normal forces and bending actions in the top and sides of prior art overfilled arch systems to an acceptable level, the radius of the arch is in practice restricted. This restriction in arch radius leads to a higher “rise” R1 and R2 (vertical dimension between the top of clearance profile C1 and C2 of lower pathway surface LS1 or LS2 and crown CR1 and CR2 of the arch) in the arch profile than is often desirable for the economical and practical arrangement of the two pathways and formation of the works surrounding and covering the arch. This results in a lost height LH1 and LH2 which can be substantial in some cases.
Beams or slabs, while needing a larger thickness than arches, do not require that “rise” and, therefore, can be used for bridges accommodating a smaller height between the top of the clearance profile of the lower pathway and the top of the upper pathway. Arches, despite their economical advantage, often cannot compete with structures using beams or slabs for this reason, especially for larger spans. However, the larger thickness may result in an expensive structure whose precast elements may be difficult, unwieldy and heavy to transport to a building site. Thus, many of the advantages of this structure may be offset or vitiated.
Furthermore, as indicated in FIGS. 1A-1C, foundations F1 and F2 for the prior art overfilled arch systems must be substantial in order to carry the arch loading indicated in FIG. 1C as AL, and require additional excavation at the base of the arch (generally beneath the lower pathway) to enable their construction. As will be understood from the present disclosure, forces AL can be considered as being circumferential forces, and forces AV can be considered as being vertical forces with forces AH being considered as horizontal forces. Loading forces on the system are a combination of these forces.
For overfilled arches made of precast construction, the incorporation of the required height of the sides or sidewalls of the arch result either in a tall-standing precast element which is difficult and unwieldy to transport and to place and/or in the requirement of pedestals, such as pedestals F1a shown in FIG. 1A.
As discussed above, transportation and handling of precast arch elements of some arch structures are difficult. However, precast elements have certain advantages including the ability to support their own self-weight and all of the advantages associated with pre-casting of such structural elements. However, precast elements also have certain disadvantages, including the transportation issues mentioned above.
Therefore, it would be helpful to retain as many of the advantages associated with precast structural elements as possible while eliminating, or at least substantially reducing, as many of the disadvantages associated with precast structural elements as possible.
Likewise, cast-in-place structural elements have many advantages, including the ability to be customized on site and the elimination of the transportation problems associated with precast structural elements. However, cast-in-place structural elements also have certain disadvantages, including a need for a formwork support structure, as well.
Therefore, it would be expedient to retain as many of the advantages associated with cast-in-place structural elements as possible while eliminating, or at least substantially reducing, as many of the disadvantages associated with cast-in-place structural elements as possible.
The referenced co-pending patent application discloses and teaches a means and method of forming an arch structure system that overcomes problems associated with the mechanical inadequacy of normal soil to support bridge and other structures of interest to that, and to this, invention. The advantages associated with the means and method disclosed in the referenced co-pending patent application are substantial. Therefore, it would be valuable to utilize the teaching of the referenced co-pending patent application in a manner which also realizes the advantages associated with the retention of the advantages associated with both precast and cast-in-place overfilled arch structures while reducing, or possibly eliminating, many of the disadvantages associated with such precast and cast-in-place structures.
While the advantages associated with the means and method disclosed in the referenced co-pending patent application are substantial, it would be extremely beneficial if further advantages in support could be realized.
Bending moments applied to an overfilled bridge structure are induced by the overfill and loads, such as traffic, carried by the bridge structure. These bending moments must be accommodated by the bridge structure. Prior overfilled structures counter these bending moments by increasing structural thickness, providing larger amounts of steel reinforcement and/or by increasing the size and stiffness of the arch supports. These measures may be costly and may not be as efficient as possible.
Therefore, there is a need for a means for efficiently minimizing bending moments induced in an overfilled arch structure.
The technology disclosed and taught in the referenced co-pending patent application significantly improves the efficiency of an overfilled bridge structure in accommodating such loading over prior art structures. However, it would be helpful if these load accommodating efficiency advantages could be further improved.
Overfilled arch structures, in particular overfilled flat arches, are sensitive to outward displacement of the arch ends. This outward displacement leads to increased bending moments in the arch. Prior overfilled structures counter these bending moments by increasing structural thickness, providing larger amounts of steel reinforcement and/or by increasing the size and stiffness of the arch supports. These measures may be costly and may not be as efficient as possible.
Therefore, there is a need for a means for efficiently reducing the outward displacements, and particularly the sensitivity of an overfilled arch to outward displacements, of arch footings.
The technology disclosed and taught in the referenced co-pending patent application significantly improves the efficiency of an overfilled bridge structure in preventing such footing outward displacement as compared to prior art structures. However, it would be helpful if these resistances to arch footing outward displacement are further improved.